1. Field of the Invention
The present invention relates to an electro-optical device, typically an EL (electroluminescence) display device, and an electronic device (electronic equipment) having the electro-optical device as a display.
2. Description of the Related Art
The development of electro-optical devices, typically EL (electroluminescence) display devices using organic material for electroluminescence, has been proceeding at a rapid pace in recent years. There are two types of EL display devices, passive matrix type EL display devices and active matrix type EL display devices.
Regardless of whether a passive matrix type or an active matrix type, the EL display device has a capacitor structure with an EL layer sandwiched by a cathode and an anode (an element having this type of structure is referred to as an EL element throughout this specification), and the EL display device operates under the principle of causing the EL layer to luminesce by the flow of electric current. A metallic electrode is generally used for the cathode, which is an electron supply source, and a transparent conducting film is generally used for the anode, which is a hole supply source. This is done because if one of the pair of electrodes is not transparent, the light emitted from the luminescing layer cannot be extracted.
In this case, the light emitted by the EL layer is directly output to the anode side, and light directed toward the cathode side is also output to the anode side after being reflected by the cathode. In other words, it is necessary for an observer to view the display device from the anode side.
However, light having a wavelength corresponding to the material of the luminescing layer can be seen from a portion of the EL layer emitting light, but in a portion of the EL layer not emitting light, the surface of the back surface side of the electrode (light emitting layer side) can be seen through the anode and the EL layer. This means that the back surface of the electrode therefore functions as a mirror, and the face of the observer is reflected.
In order to avoid this, a method of attaching a circular polarization film to the EL display device so that the observer""s face is not reflected is employed, but there is a problem in that the circular polarization film is extremely high cost, therefore leading to increased manufacturing costs.
The present invention is made in view of the above problems, and an object of the present invention is to prevent an EL display device from becoming mirrored, and to provide a low cost EL display device in which the EL display device manufacturing cost has been reduced. In addition, an object of the present invention is to lower the cost of an electronic device having a display using the EL display device.
The present invention is characterized in that a projecting portion is formed on a reflecting surface of a cathode (a surface contacting a luminescing layer side), and light reflected by the reflecting surface of the cathode is scattered. Namely, the present invention is characterized in that the reflecting surface of the cathode is made not visible to an observer by diffusely (irregularly) reflecting visible light (external light) incident from an anode side by-using the reflecting surface of the cathode.
The textured portion formed on the reflecting surface of the cathode may be formed by concave shape depressions, or by convex shape projections. Further, a wave shape surface in which the unevenness is repeated may also be used. The projecting portion may be formed by a technique such as photolithography or holography (for example, a technique of forming an uneven reflecting structure recorded in Sharp Technology Reports, No. 74, pp. 16-9, August 1999), and may also be formed by surface processing, such as plasma treatment or etching. Further, the projecting portion may also be naturally generated in the surface by using the film deposition conditions of the cathode (or a base electrode).
In other words, the formation of the projecting portion may be regulated or unregulated, but it must be formed so as to average a diffused reflection (irregular reflection) within the surface of a pixel. A structure in which the projecting portion is formed as explained above is referred to as a textured structure throughout this specification.
Further, by forming projecting portions in other thin films contacting the cathode, and then forming the cathode on top, the projecting portion can be formed in the reflecting surface of the cathode. In particular, Japanese Patent Application Laid-open No. Hei 9-69642 and Japanese Patent Application Laid-open No. Hei 10-144927 can be cited for means of forming the projecting portion in an aluminum film. Namely, by forming the aluminum film based on the above patent applications, and by laminating the cathode on top of the aluminum film, it is possible to obtain a cathode having the projecting portion.